Catalytic process for the preparation of light olefins from methanol in fluidized bed reactor

ABSTRACT

Methanol is converted in light molecular olefins C 2 -C 4  with 93-100% degree of transformation and more than 90% selectivity in which more than 80% are ethylene and propylene upon a microspherical catalyst based on SAPO-34 zeolite, with continuous reaction-regeneration in a fluidized bed reactor-regenerator system. Ethylene/propylene ratio is changed in relatively large limits 0.69-1.36, by the modification of reaction temperature and space velocity of the feed.

This is a National Stage entry under 35 U.S.C. § 371 of Application No.PCT/RO99/00001 filed Jan. 11, 1999, and the complete disclosure of whichis incorporated into this application by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a process for conversion of methanol toolefins using SAPO-34 zeolite in fluidized bed reactor with continuousregeneration of catalyst.

2. Background Art of the Invention

Light olefins, namely ethylene and propytene, are important rawmaterials for polymers production.

Industrial, ethylene and propylene are obtained by steam cracking ofC₂-C₄ paraffins and petroleum fractions in so called hydrocarbonspyrolisis process. The continuous rising of olefins requirement with theoil reserve shortage in the future make interesting the researches fornew olefins manufacture technologies from non petroleum raw materials.

One of the more attractive method for C₂-C₄ olefins production is basedon catalytic conversion of methanol because methanol is manufactured inadvanced technologies with very high capacity till 800,000 mt/year asingle line and has wide raw materials availability like natural gasesincluding methane, coals and renewable biomass.

Methanol conversion into light olefins with industrial accepted yieldswas possible only after the synthesis of high silica zeolite ZSM-5 byMobil Oil's researchers (U.S. Pat. No. 3,702,886). After this many othertypes of zeolites were tested in the reaction of methanol to olefinslike ZSM-34 (U.S. Pat No. 4,079,096), Mordenite (Ro Patent 87685, U.S.Pat No. 3,244,766), Offretite (U.S. Pat No. 4,079,096) arseno-silicates(Ger. Off. 2830830), boro-silicates (Ger. Off. 2830787). Methanolconversion to olefins is claimed also in many patents based onsynthtetic alumino-silicates like U.S. Pat Nos. 4,062,905, 3,979,472,3,911,041 and Ger. Off. 2755299, 2615150.

These catalysts exhibit low selectivities in olefins and must beperiodically regenerated with air at 470-570° C.

Numerous methods for modification of zeolites and reaction conditionswere elaborated for olefins selectivity rising and increasing the activecycle of the catalysts. Interesting results were obtained by zeolitesilification (U.S. Pat. Nos. 4,100,219, 4,145,315), increasing Si/Alatomic ratio by aluminium extraction (U.S. Pat. No. 4,447,669, Ger. Off.2935863), ionic exchange or impregnation with Cs, Ba, Pb, TI (U.S. PatNo. 4,066,714), B, Mg (U.S. Pat No. 4,049,573, Ger. Off. 3300892), Hf,Zr (U.S. Pat No. 4,481,376, Ger. Off. 3300982), dilution of the catalystwith inert materials (U.S. Pat No. 4,025,572), partial deactivation withsteam (UK Patent 2127036) or HF (U.S. Pat No. 4,486,617). Good resultshave given complex treatments with Mg—Mg or Mg—Sb (RO Patent 87413).Some reaction parameters were also modified, for instance underatmospheric pressure utilization (U.S. Pat No. 4,025,575), steamdilution of feed (U.S. Pat No. 4,083,889) or dilution with air (U.S. PatNo. 4,433,189), oxygen (U.S. Pat. No. 4,049,735) and aldehyde (U.S. PatNo. 4,374,295). The synthesis by Union Carbide Corporation's researchersof Si—Al—P zeolites named SAPO-zeolites (U.S. Pat Nos. 4,310,440,4,440,871) has opened new perspectives for methanol conversion toolefins, MTO-process. As the Chinese researchers have demonstrated forthe first time onto SAPO-34 zeolite it obtained till 89% C₂-C₄ olefinsat practical total conversion of methanol 57-59% being ethylene andethylene/propylene molar ratio 2.24-2.31 (Applied Catalysis, Vol. 40,Nr. 1-2, 1988, p.316). Due to the catalyst coking active cycle is only1-2 hours.

The use of SAPO-34 zeolite synthesised as in U.S. Pat No. 4,440,871 rosecontradictory literature data concerning the thermal and steam stabilityand olefins selectivity. It must be also underlined that the sythesis ofthe zeolite is made with expensive materials like aluminiumisopropoxyde, tetraethylammmonium hydroxide or quinuclydine.Neutralization of the reaction mixture with NaOH has complicated thetechnology for SAPO-34 manufacture due to the necessity of ammonium ionexchange and supplementary calcination step.

Thermal analysis (Gr.Pop et al., Progress in Catalysis, Bucharest, 1,1993, p.1) showed that a good thermal and steam stability have SAPO-34zeolites with crystals smaller than 4 micrometer.

MTO—process was materialized in tubular reactors with fixed bed catalyst(U.S. Pat No. 4,590,320) and in fluidized bed reactors with catalystregeneration in fluidized bed. Vaporized methanol feed mixed with thezeolite catalyst is charged to the bottom of the riser contact zone toform a suspension for flow up wardly through the riser (U.S. Pat. No.4,328,384). The reactors with fixed bed catalyst have many desadvantagesin methanol reaction to olefins because the remove of the reaction heatis dificult and frequent catalyst regeneration diminishes productioncapacity. The increasing the coke deposits on the catalyst in the activecycle changes continuous the reaction products composition.

Fluidized bed reactors and continuous regeneration of the catalysteliminate these desadvantages but in a riser reactor the optimal ractionconditions can't be realized.

Kinetic studies in fluidized bed reaction have shown the maximumethylene formation at short reaction time of about two seconds. (C.Tsakiris et al., Proc. IFAC Symposium DYCORD 92 College Park, Md., April1992), which is not obtainable in a riser reactor. In a riser typereactor two important reaction paramiters, contact time and temperature,determining product selectivites can't be well controlled.

All as synthesized zeolite including SAPO-34, have low selectivity inmethanol conversion to olefines. By zeolite modifications itsselectivity can be increased. For example, PCT/US96/19673 teaches aprocess in which a SAPO-34 zeolite is modified by ion exchange with Niand then given a catalyst with 30% more selective in methanol conversioninto ethylene+propylene.

SUMMARY OF THE INVENTION

In the U.S. Pat. No. 5,095,163, SAPO-34 catalyst is hydrothermallytreated 3-50 hours, in air or steam, at 650-775° C., the catalystacidity decreases from about 5.2 meq.NH₃/cc 11.8 mez.NH₃/cc andselectively to C₂+C₃ olefines in methanol conversion increase from 63 to80%. U.S. Pat. No. 4,873,390 uses a selective cocking of the SAPO-34zeolite till 5-30% coke in the catalyst to improve the methanoltransformation in ethylene from 6.04% to 46.65% and in propylene from15.43% to 50.60%. Maximum ethylene+propylene selectively obtained is83.7%.

The Invention eliminates these difficulties since the catalyst isobtained from cheap raw materials like industrial alumina and aqueoussilica sol and the template, tetraethylammonium phosphate is “in situ”preparated: by ethylbromide and triethylamine. The methanol conversionand continuous catalyst regeneration are conducted in fluidized bedreactors, without riser, methanol feed being injected in dense bedcatalyst.

The claimed process may find applications in the industry to obtain, bya new route more economic, ethylene and propylene, basic raw materialsfor petrochemistry and synthetic fuels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a SEM microphotography of Example 1 zeolite.

FIG. 2 shows a XRD-spectra of Example 1 sample.

FIG. 3 shows dimension distribution curves of the catalyst of Example 1.

FIG. 4 shows an installation for methanol conversion to olefines.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst synthesis made only with cheap, industrial raw materialnamely triethylamine, ethyl bromide, concentrated phosphonic acid, morethan 70 weight %, hydrated alumina and silica sol, all with very low,under 0,01% Na content. Concentrated silica sol can be stabilized withammonia. In the condition of the patent, by hydrothermal treatment ofSi—Al—P amorphous gel is obtained the active, H form of SAPO-34 zeolite,in relatively short zeolitization time. After the calcination at350-580° C. for remove the organic template, the obtained zeolite isused as catalyst. The zeolite is atomized at 400-450° C. in a silicamatrix as microspheres. The compozition of amorphous gel and thereaction condition in the crystallization, calcination and atomizationsteps assure to obtain an active and selective catalyst for methanolconversion to olefins, with a granulation curve suitable in a fluidizedbed process and with good thermal and mechanical resistance.

The process of methanol conversion to light olefins mainly ethylene andpropylene, is realized in fluidized bed, including a reactor—regeneratorsystem, with continuous circulation of the coked catalyst from reactorto regenerator and the regenerated catalyst form regenator to reactor.The methanol feed and regeneration air are injected in the dense bed ofthe catalyst. This system assures constant temperature in the catalystbeds and contact time of about two seconds. The reactor and regeneratorrisers only hinder the fluxes reversing. By steam or nitrogen purging inthe risers, the catalyst is purified by the methanol and hydrocarbonsadsorbed in reactor and oxygen adsorbed in regenerator. So the loss ofmethanol by burning in a regenerator is avoided. Also is avoided theburning of the methanol in the reactor by the oxygen adsorbed on thecatalyst in regenerator. The purging of the catalyst assures a very lowcarbon oxydes in the reaction products with a supplementary reduction ofthe costs for olefins separation. To keep constant the catalyst activitya small amount is removed from reactor or regenerator in parallel withadding an equal quantity of fresch catalyst. The reactor and regeneratorhave interior devices for taking-over the heat reactions of methanolconversion and coke burning.

The following examples illustrate, but not limit, the present invention.

EXAMPLES Example 1

By known method is prepared a tetraethylammonium phospate, aqueoussolution 25%, from triethylamine, ethylbromide and phosphoric acid 73%.

Hydrated alumina 65% Al₂O₃ with 40% bayerite, is suspended indemineralized water and is charged, under stirring in a 3500 I autoclaveover tetraethylammonium phosphate solution and then is added the 28%SiO₂ silica sol stabilized wih ammonia. Th pH of resulted suspension isfixed at 6.3-6.5 with phosphonic acid.

Molar ratio of the component in the suspension is:

P₂O₅:Al₂O₃:SiO₂:TEAOH 1:1.5:0.37:1.1.

Zeolitization is made in six succesive steps: the first step of thecristallization begins with 15% of the whole suspension at 198-205° C.After 20 hours the autoclave is cooled at 30-40° C. and a new quantityof suspension is added. The zeolitization process is resumed in the sameconditions. The operation is repeated five times. The entirezeolitization process, including intersteps cooling, is about 100 hours.

Analytical control, by XRD technique, of the product obtained shows morethan 90% SAPO-34 zeolite and about 7% unreacted bayerite.

In Table 1 are shown the characteristic bands in the XRD—spectrum of theSAPO-34 zeolite obtained, and SAPO-34 spectrum reported in U.S. Pat. No.4,440,871, for comparison.

TABLE 1 Characteristic bands in XRD-spectrum (Cu lamp, Cu k_(α) =1.5418) U.S. Pat. No. 4440871 Sample, Example 1 2θ d, Å 100 Xi/l_(o) 2θd, Å 100 Xi/l_(o) 9.45-9.65 9.36-9.17  81-100 9.63 9.18 100  12.8-13.056.92-6.78  8-20 12.87 6.88 18 13.95-14.20 6.35-6.24  8-23 14.17 6.25 2116.0-16.2 5.54-5.47 25-54 16.16 5.4 47 17.85-18.15 4.97-4.89 11-26 18.34.89 22 19 4.67 0-2 — — — 20.55-20.9  4.32-4.25  44-100 20.67 4.3 9722.05-22.50 4.03-3.95 0-5 22.33 3.98 4  23.0-23.15 3.87-3.84  2-10 23.153.84 8 24.95-25.4  3.57-3.51 12-87 25.38 3.52 26 25.8-26.0 3.45-3.4314-24 25.97 3.43 17 27.5-27.7 3.243-3.220 1-4 27.68 3.22 4 28.05-28.4 3.181-3.143  1-12 28.4 3.14 4 29.2-29.6 3.058-3.018 3-9 29.15 3.06 430.5-30.7 2.931-2.912 19-75 30.67 2.91 29 31.05-31.4  2.880-2.849 15-2831.25 2.86 22 32.2-32.4 2.780-2.763 1-5 32.42 2.76 3  33.4-33.852.683-2.648 0-6 33.66 2.66 4 34.35-34.65 2.611-2.589  4-15 34.48 2.6 736.0-36.5 2.495-2.462  2-11 36.33 2.47 4 38.8-38.9 2.321-2.315 0-2 38.82.32 2 39.6-39.7 2.276-2.070 2-4 39.76 2.27 5

The crystallite dimensions are between 1 and 3 micrometer (FIG. 1). Thezeolite is stable by calcination and in air and steam, as is shown inFIG. 2.

In the zeolitization phase results a zeolite suspension with 16.7% solidwich is separated with 6.7 I/m² hours filtration rate. After washingwith demineralized water and air drying results a paste of zeolite with57% humidity.

The humid paste of zeolite is mixed with 28% SiO₂ Silica sol stabilizedwith ammonia in weight ratio zeolite: SiO₂ 60-40, fixed at pH 6.3 withnitric acid 40% and atomized under pressure with 400-450° C. hot air atentrance and 175-180° C. at exit. Injection pressure is 4-4.5 bars andthe productivity of atomizer 50 kg/hour dry catalyst. Finaly thecatalyst is calcined with a heating rate of 100° C./min. at two constantlevel, three hours at 350-400° C. and ten hours at 580° C. The coolingtime of the catalyst is 4 hours. All the raw material used for catalystpreparation have a Na content under 0,01%. The microspherical catalystobtained has good flow preperty and granulation curve showed in FIG. 3.

FIG. 4 is a schematic flow chart of the reaction—regeneration with fluidbed catalyst system for methanol conversion to olefins, MTO process,part of invention. With reference to FIG. 4, the reactor R1 is filledwith 100 I catalyst and the regnerator R2 with 30 I catalyst. Byfluidization is taked form the dense fluid bed catalyst 2-2′ and upperinterface 3-3′. The temperature of dense fluid bed catalyst in R1 isfixed at 440° C. and in R2 at 480-610° C. The temperatures in R1 and R2are controlled by circulating heatin—cooling agent in interior heatexchangers 9-9′. Methanol and regenerating air are fed throughconnection 5-5′ and sieves 4-4′ with 100 l/hour respectively 1000Nl/hour.

The circulation of the catalyst between reactor and regenerator isrealized by nitrogen as lift gas through transfer lines 12-12′.Automatic control level of catalyst bed in R1 and R2 is made by keepconstant the pressure drops with regulators 11-11′, which act thecatalyst flow rate regulating valves 10-10′. Reaction products andcatalyst entrained are evacuated at the top of R1 and R2 and separatedin cyclone systems 6-7 and 6′-7′. Through the conduits 8-8′ theentrained catalyst is recycled in the reactor-regenerator reaction zone.About 2 kg catalyst is withdrwn from the bottom of separation cyclone 7or 7′ in each 48 hours and is replaced with the same quantity of freshcatalyst through the charge device 15 or 15′. So the irreversibledesactivation of the catalyst is compensated.

The coked catalyst in the conduite 13 has 4.3 wt. % coke and theregenerated catalyst in conduite 13′ has a coke retention level of 1.7wt. %. Reaction products after the exit from cyclone 7 are cooled inheat exchanger 14 and separated in the separation vessel 16 into anoncondensed hydrocarbon fraction and a liquid fraction wich containsthe process water, dimethylether and unconverted methanol. The gaseoushydrocarbon fraction is sent to a conventional olefins separation unit.From liquid fraction is separated by distillation dimethyleter andmethanol wich are recycled to the reactors R₁.

Regeneration gases after cooling in heat exchanger 16′ and washing inthe column 14′ are evacuated in the atmosphere.

The composition of the fluxes are shown in Table 2.

TABLE 2 Effluent composition obtained in Example 1. Uncondensed LiquidRegeneration organic phase phase gases, exit vessel 16 vessel 16 cyclone7′ Component wt. % wt. % wt. % Oxygen — — 1.5 Nitrogen — — 82.7 Carbonmonoxyde — — 4.3 Carbon dioxyde — — 11 Hydrogen 0.2 — 0.5 Methane 1.6 —— Ethane 0.3 — — Ethylene 46.8 — — Propane 2.5 — — Propylene 40 — —Butanes 0.53 — — 1-Butene 1.74 — — iso-Butene 0.71 — — 2-Butenes 4.04 —— C₅ + hydrocarbons 1.58 — — Methanol —  0.5 — Dimethylether — — — Water— 99.5 —

Example 2

Using the catalyst and installation of Exemple 1 by temperature andspace velocity modification the ethylene/propylene ratio is changed inrelatively large limits of 0.69-1.29.

Some illustrating results are shown in Table 3.

TABLE 3 Reaction products compositions, in different reactionconditions. Experience number 1 2 3 4 5 6 a. Reaction conditionsTemperature, 400 405 410 435 470 490 ° C. LHSV, h⁻¹ 1.1 0.6 1 1.9 1.52.7 b. Un- condensed organic phase analysis, wt. % Hydrogen 0.08 0.230.13 0.12 0.71 0.1 Carbon oxydes — — — 0.14 0.21 — Methane 0.62 1.780.81 1.12 2.42 0.91 Ethane 0.26 0.9 0.42 0.64 — — Ethylene 28.3 48.534.1 43 42.45 36.8 Propane 2.3 5.3 2.4 2.43 5.9 2.27 Propylene 41.2 35.742.9 42 32.95 45.4 Butanes 0.9 0.88 0.8 0.68 0.8 0.72 1-Butene 1.94 1.191.75 1.63 1.94 1.7 iso-Butene 0.77 1.23 0.75 0.44 1.04 0.2 2-Butenes7.22 2.56 6.68 4.87 7.13 5.2

REFERENCES

1. Brent M. Lok, Celeste M. Messina, Robert L. Pation, Richard T. Gajek,Thomas R. Cannan, Edith M. Flanigen (Union Carbide Corporation), U.S.Pat. No. 4,440,871 (Apr. 3, 1984), Int. Cl. B01 j 27/14; U.S. Cl502/241.

2. Ajit V. Sapre (Mobil Oil Corporation), U.S. Pat. No. 4,590,320 (May20, 1986), Int. Cl. Co7C1/20; U.S. Cl.585/324; 585/315

3. Nicholas Davidiuk, James Haddad (Mobil Oil Corporation) U.S. Pat. No.4,328,384 (May 4, 1982), Int. Cl. C 97c1/20, U.S. Cl. 585/469; 585/639;585/733.

Experience Number 1 2 3 4 5 6 C₅ + Hydrocarbons 2.41 0.95 2.84 1.58 4.451.75 Dimethylether 14.00 0.78 6.42 1.35 — 4.95 c. Liquid phase analysis,wt. % Dimethylether 1.5 — 0.5 — — — Methanol 12 3 9 1.5 0.1 1.5 Water86.5 97 90.5 98.5 99.9 98.5 d. Coke deposits on the catalyst, wt. %Reactor R₁ exit 4.9 5 4.8 4.5 4.6 4.7 Regenerator R₂ exit 1.2 2.8 0.60.9 1.2 1.9 e. Ethylene/propylene ratio 0.69 1.36 0.79 1.02 1.29 0.81 f.Methanol conversion 93.3 98.3 95 99.2 100 99.2

What is claimed is:
 1. A method for the preparation of light olefinsfrom methanol conversion using a microspherical catalyst comprisingSAPO-34 zeolite, and the method comprising the step of contactingmethanol with a fluidized or moving bed of said catalyst and beingcharacterized in that said SAPO-34 zeolite is prepared from alumina,silica and a preformed template tetraethylammonium phosphate.
 2. Amethod according to claim 1 comprising the further steps of:continuously regenerating the catalyst of said bed with air, andsubstituting a portion of regenerated catalyst with fresh catalyst inorder to keep constant the activity and selectivity of the catalyst. 3.A method according to claim 2, in which the regeneration with air isperformed at 480-610° C.
 4. A method according to claim 2, in which thecontacting and the regeneration steps are performed in a reactor and aregenerator respectively with continuous circulation of the catalystbetween said reactor and said regenerator.
 5. A method according toclaim 1, in which methanol is contacted with said catalyst at atemperature of 400-490° C. and liquid space velocities of 0.6 to 2.7h⁻¹.
 6. A method according to claim 1, in which the preformed templatetetraethylammonium phosphate is prepared from triethylamine,ethylbromide and phosphoric acid.
 7. A method according to claim 1 inwhich the microspherical catalyst is obtained by the steps of: atomizinga mixture of said SAPO-34 zeolite and silica under pressure and at400-450° C. to form microspheres.